Engineering Faceted Nanoporosity by Reactions in Thin-Film Oxide Multilayers in Crystallographically Layered Calcium Cobaltate for Thermoelectrics

Introducing porosity is attractive for tailoring electronic, thermal, and mechanical properties of inorganic materials. Nanoporosity typically either inherent in crystallographic channels the structure or obtained by external templating during synthesis sintering. However, controllably engineering materials with laminated crystal structures without remains a challenge. Here, we demonstrate realization faceted oriented nanopores textured Ca3Co4O9—a ceramic misfit-layered importance thermoelectric applications—from chemical reactions CaO/Co3O4 multilayers. We show that CaO conversion to Ca(OH)2 cobalt oxide stoichiometry are key determinants nanoporosity. Adjusting unreacted fraction alters nanopore size Ca3Co4O9. The preferred orientation Ca3Co4O9 underpinned texture reactant multilayers reactant–product relationships density difference. Oriented pore formation attributed basal plane removal driven local densification nuclei through growth impingement. These findings point possibilities nanoporosity variety structures.